This invention relates to computer memory devices having address control function. By constructing a bitmap plane using these memory devices, the data transfer speed between bitmap areas can be improved because the data can be read and written with 8 bits or 16 bits width regardless the byte boundary in the bitmap plane.
While computer techniques have been developed on the basis of the numeric and character data processing hitherto, recently, due to the enhancement of the processing capacity of microprocessors and to the drop in price of memory chips, there is being developed a type of workstation which can process image information in addition to color information.
Since the workstations generally employ color and monochrome high resolution monitors having resolution of the degree of 1000 pixels.times.1000 pixels instead of ASCII terminals which can display only the character information, it necessarily requires the functions for processing a large number of image informations at high speed.
One of such image processing functions is BITBLT(BIT Boundary Block Transfer) function, that is, function of transferring data in the particular area of the bitmap consisting of a number of memories to the other area.
In the workstation, window function or graphic function is performed by means of such BITBLT function, and the processing speed in performing such BITBLT function is an important factor in determining the general performance of workstation. Accordingly, in general, the appropriate graphic pocessors are used in workstations in order to enhance the image processing speed.
However, because the conventional memory devices have been developed with the type suitable to process character information as a unit of byte, in the case of construction of bitmaps with these memories, CPU(Central Processing Unit) or graphic processor can handle only 8 bit or 16 bit data corresponding to same address simultaneously. So, in order to extract the useful data from it, CPU or graphic processor must pick out the desired data by shifting 8 bit or 16 bit data left or right. Because the processing procedures become more complex, the processing speed and the efficiency are degraded.